Undercarriage for adverse terrain vehicles

ABSTRACT

An undercarriage for adverse terrain vehicles comprises an elongate hollow load-bearing frame having at least three axles rotatably supported thereon. The axles support wheel members and each middle wheel member is positioned below the endmost wheel members to facilitate skid steering. The axles are drivingly interconnected by a transmission which may comprise: one or more planetary gear sets; one or more differential gear sets; one or more chain and sprocket drives; one or more idler gears; one or more drive shafts; and combinations thereof.

CROSS REFERENCE TO RELATED APPLICATION

This is a continuation of application Ser. No. 115,942 filed Jan. 28,1982 now abandoned. Which is a continuation-in-part of co-pendingapplication Ser. No. 11,857, filed Feb. 13, 1979, now U.S. Pat. No.4,210,218, which is a continuation of application Ser. No. 799,328,filed May 23, 1977, abandoned.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates generally to undercarriages for adverse terrainvehicles, and more particularly to a detachable undercarriage havingeither three or four tired wheels which may be utilized to support andpropel virtually any type of mechanism.

Traditionally, adverse terrain vehicles have been track type vehicles.For example, track type bulldozers, loaders, cranes, and similar deviceshave been known for decades. In some instances track type mechanisms ofthis type have utilized undercarriages to suppot and propel themechanism. Such an undercarriage may comprise a frame for attachment tothe mechanism, structure mounted on the frame for guiding a track arounda predetermined course, and a drive motor for actuating the track aroundthe course and thereby propelling the mechanism supported by theundercarriage.

More recently, adverse terrain vehicles utilizing tired wheels have beendeveloped. For example, see U.S. Pat. No. 3,799,362 granted toApplicants herein on Mar. 26, 1974. However, there has not heretoforebeen provided an undercarriage whereby a tired type vehicular supportingand propelling apparatus adapted for adverse terrain usage could beadapted to virtually any type of mechanism. It has also been found to bedesirable to provide a tired type adverse terrain undercarriage havinggreater load carrying capacity than has been available heretofore.

The present invention comprises a detachable undercarriage for adverseterrain vehicles which overcomes the foregoing and other problems longsince associated with the prior art. In accordance with the broaderaspects of the invention, an undercarriage includes an elongate hollowframe having a plurality of axle members rotatably supported thereon.Each axle member extends to a wheel support member. Solid or pneumatictired wheels can be utilized. Preferably all the wheel support membersare positioned on the same side of the frame. A transmission, such as achain and sprocket drive apparatus, rotatably interconnects at least twoof the axle members, and the frame can comprise a lubricant reservoirwhereby the transmission is continually operated in a lubricant bath. Adrive assembly includes a motor mounted on the frame and a drivesprocket and chain connecting the output of the motor to one of the axlemembers. The motor can be of either the hydraulic or the electricvariety. More than one motor can be utilized to drive the undercarriage,if desired. A brake assembly includes a brake disc mounted on at leastone of the axle members and a plurality of brake pucks for frictionallyengaging the brake disc, or a hydraulic brake mounted between the motorand the speed reducer.

Either three or four nonaligned axle members carrying wheels of equaldiameters can be utilized. In the case of three axle members the centeraxle member and in the case of four axle members the center two axlemembers rotate about axes situated below a plane extending through theaxes of rotation of the endmost two axle members. This facilitates theskid steering of a mechanism supported and propelled by theundercarriage, while simultaneously making wheels carried by all of theaxle members available for ground contact under adverse terrainconditions. If desired, structure may be provided for bringing all ofthe axle members into alignment in order to provide increased stability.

Either three or four aligned axle members carrying wheels of unequaldiameters can be utilized. The center axle in the case of three axlemembers and the center pair of axles in the case of four axle memberscarry wheels relatively larger than those carried by the endmost axlemembers. The same result is accomplished, namely the facilitation ofskid steering of the mechanismm supported and propelled by theundercarriage with the concurrent availability for ground contact underadverse terrain conditions of all the wheels.

In accordance with still other aspects of the invention, the frame is ahollow load-bearing structure comprised of structural members around itsentire periphery and throughout its entire length. This facilitatesattachment of a mechanism to the undercarriage at any point along theentire length and around the entire periphery of the frame. Thepositioning of the hydraulic or electric motor relative to the frame canbe varied in order to vary the spacing between the axle members. Themotor is preferably drivingly connected to one of the axle members bymeans of a first drive sprocket connected to the output of the motor, asecond drive sprocket connected to one of the axle members, and a drivechain interconnecting the two drive sprockets. In other embodiments ofthe invention, gears or drive shafts are employed to drivinglyinterconnect the axle members. One or more motors coupled directly tothe axle members can also be utilized, if desired.

DESCRIPTION OF THE DRAWINGS

A more complete understanding of the invention may be had by referringto the following Detailed Description when taken in conjunction with theaccompanying Drawings, wherein:

FIG. 1 is a side view of an undercarriage for an adverse terrain vehicleincorporating a first embodiment of the invention;

FIG. 2 is a top view of the undercarriage shown in FIG. 1 in whichcertain parts have been broken away more clearly to illustrate certainfeatures of the invention;

FIG. 3a is an enlarged horizontal sectional view of the rear portion ofthe undercarriage of FIG. 1;

FIG. 3b is an enlarged horizontal sectional view of the front portion ofthe undercarriage of FIG. 1, and comprising a continuation of FIG. 3a;

FIG. 4 is a side view of a first modification of the undercarriage ofFIG. 1;

FIG. 5 is a side view of a second modification of the undercarriage ofFIG. 1;

FIG. 6 is a side view of the speed shifter assembly mounted on thehydraulic motor of the undercarriage of FIG. 1;

FIG. 7 is a side view of the undercarriage for an adverse terrainvehicle incorporating a second embodiment of the invention;

FIG. 8 is a top view of the undercarriage shown in FIG. 7;

FIG. 9 is a diagrammatic illustration of a portion of a hydrostaticdrive control apparatus useful in conjunction with the presentinvention;

FIG. 10 is a detail of a wheel height adjustment assembly which may beused in conjunction with the invention;

FIG. 11 is an illustration of the application of the invention to afront-end loader;

FIG. 12 is an illustration of the application of the invention to afront-end loader with a backhoe;

FIG. 13 is an illustration of the application of the invention to amobile drilling rig;

FIG. 14 is an illustration of the application of the invention to abackhoe;

FIG. 15 is a side view of a third modification of the undercarriage ofFIG. 1;

FIG. 16 is a top view of the undercarriage shown in FIG. 15 in whichcertain parts have been broken away to illustrate more clearly certainfeatures of the invention;

FIG. 17 is a side view of an undercarriage for an adverse terrainvehicle incorporating a third embodiment of the invention;

FIG. 18 is a side view of an undercarriage for an adverse terrainvehicle incorporating a fourth embodiment of the invention;

FIGS. 19-23 are additional modifications (some partially cut away) ofthe three-wheel undercarriage shown in FIGS. 1 and 15; and

FIG. 24 is a partial section view of the transaxle utilized in themodified undercarriages of FIGS. 22 and 23.

DETAILED DESCRIPTION

Referring now to the Drawings, wherein like reference numerals designatelike or corresponding elements throughout the several views, andparticularly referring to FIGS. 1 and 2 thereof, there is shown adetachable undercarriage for an adverse terrain vehicle 10 incorporatingthe invention. Normally, of course, a pair of parallel undercarriages 10are employed to support the adverse terrain vehicle. The undercarriage10 consists of an elongate hollow load-bearing frame 12. Frame 12 isformed entirely of a material such as steel characterized by highstrength and rigidity to permit attachment of undercarriage 10 tovirtually any type of mechanism by connections at selected points alongthe entire length and around the entire periphery of frame 12. A relatedfeature of this structure is greater load carrying capacity.Furthermore, frame 12 can be of sealed construction so that it can serveas a lubricant reservoir, if desired, as well as a structural member.Drain plugs 14 and 16 are located at the bottom and outside surfaces,respectively, of frame 12 to facilitate draining or replenishing oflubricants therein.

The undercarriage 10 is supported by three tired wheels 18; the threewheels including a forward wheel 20, a middle wheel 22, and a rear wheel24. The wheels 18 are of equal diameter and include tires of either asolid or a pneumatic type. Wheels 18 rotate about axles 26. Preferablyall three wheels 18 are positioned on the same side of frame 12;however, depending on the particular adverse terrain vehicle, it may bedesirable to locate one wheel 18 on the opposite side of frame 12.Preferably, axles 26 extend completely through frames 12 and arerotatably supported within both adjacent vertical surfaces of frame 12.

Also included in undercarriage 10 is drive assembly 28. Drive assembly28 incorporates a motor 30 which can be of a dual speed variety in thatstructure is provided within motor 30 for selecting either a high or lowspeed range of operation. Such selection is effected by manipulation oflever 32. Alternatively, motor 30 can be of the constant speed variety.In addition, motor 30 can be of the electric or the hydraulic types.Referring momentarily to FIG. 6 in conjunction with FIGS. 1 and 2,undercarriage 10 is provided with a fluid operated cylinder 34 having apiston 36 connected to lever 32 by means of link 38. Cylinder 34 isadapted for operation from a remote point, such as the operator'scompartment of an adverse terrain vehicle incorporating undercarriage10, to selectively place motor 30 in the desired operational range.

Referring again to FIGS. 1 and 2, motor 30 is connected directly tospeed reducer 40, which can be a multiple or constant speed type. Speedreducer 40 is slidably mounted on frame extension 42 by means of bolts44. Frame extension 42 extends upwardly from the inside rearward topsurface of frame 12 and speed reducer 40 is bolted substantiallyperpendicular thereto. Speed reducer 40 has output shaft 46 to whichdrive sprocket 48 is attached by means of setscrew 49, as is best shownin FIG. 3a. If, for example, motor 30 is of the hydraulic type, motiveenergy is received from the output of remotely located hydraulic pumps(not shown) driven by an engine mounted on the adverse terrain vehicleto which undercarriage 10 is attached. The power transmission by meansof the pressurized hydraulic fluid from the aforementioned pumps, orfrom a remote power source (not shown) in the case of an electric motor,to motor 30 and hence to drive sprocket 48 through speed reducer 40comprises the hydrostatic drive system which functions to both propeland steer undercarriage 10.

Motive power is first applied to drive sprocket 48 which is constrainedto second sprocket 50 by means of chain 52. Chain 52, which isconstrained around drive sprocket 48 and second sprocket 50, serves totransfer rotative movement to axle 26, upon which first sprocket 50 ismounted. Sprockets 48 and 50 and chain 52 are totally enclosed in asealed housing 54 which is detachably secured to both frame extension 42and frame 12. Housing 54 serves not only to protect these parts of thedrive system, but more importantly, can constitute a reservoir forlubricant in which chain 52 and sprockets 48 and 50 continuouslyoperate. Accordingly, drain plug 56 is provided at the rearward lowerend of housing 54.

A tension adjusting means for chain 52 is provided in bolt 58. Bolt 58is threadably mounted on brace 60 and acts in compression directlyagainst the collar of speed reducer 40, which is slidably mounted onframe extension 42. Thus, by either clockwise or counterclockwiserotation of bolt 58, tension in chain 52 may be varied.

Motor 30 is in direct operative relationship with the forward, middleand rearward wheels, 20, 22 and 24, respectively, of undercarriage 10.Constituting part of the drive system, axle 26 of rear wheel 24 receivespower by means of first sprocket 50 which is connected to drive sprocket48 by means of chain 52. Also attached to axle 26 of rear wheel 24 issprocket 62. Sprocket 62 is coupled by means of chain 64 to sprocket 66,which is connected to the axle 26 of middle wheel 22. Sprocket 68 isalso attached to the axle 26 of the middle wheels 22 of the set, and inturn is coupled by means of chain 70 to sprocket 72. Sprocket 72 issecured to the axle 26 of the forward wheel 20 of the set, whereby motor30 is operatively connected to all three wheels 18 on undercarriage 10.Tension adjustment assemblies 74 are provided for assuring propertension in chains 64 and 70.

In order to arrest movement of undercarriage 10, brake assembly 76 isprovided. Brake assembly 76 consists of a brake disc 78 and threecaliper assemblies 80. Turning momentarily to FIG. 3b in conjunctionwith FIGS. 1 and 2, caliper assemblies 80 (only one of which is shown)are anchored to frame extension 82 by means of bolts 84. Consequently,the caliper assemblies 80 remain stationary at all times, while thebrake disc 78, which is secured to axle 26 of the middle wheel 22,rotates therewith. Specifically, brake disc 78 rotates within the slotsof the three caliper assemblies 80 which house the brake pucks and theirhydraulic actuating cylinders. To arrest movement of the undercarriage10, the actuating cylinders cause the pucks to frictionally engage discs78. By means of chains 64 and 70, this braking force is directlytransmitted to the rearward and forward wheels, 24 and 20, respectively.In this manner, the force of one brake assembly 76 is simultaneouslyapplied to all wheels on the undercarriage 10. It will be noted thatbrake assembly 76 is disposed to the interior of axle spindle 86, towhich wheel rim 88 is secured by threaded lugs 90. This location forbrake assembly 76 is advantageous in that it affords protection fromdirt, rocks, mud, or other debris typically encountered by an adverseterrain vehicle.

Middle wheel 22 protrudes below a plane 92 extending tangent to thebottom surfaces of the wheels 18 comprising the forward wheel 20 and therear wheel 24. This fact embodies a significant feature of the presentinvention. A relatively short wheelbase is desirable because itfacilitates skid steering of the vehicle. However, this advantage isoffset by decreased overall vehicle stability, which is especiallytroublesome in the case of an adverse terrain vehicle with variableloading arrangements. In contrast, a longer wheelbase affords maximumvehicle stability but does not permit effective skid steering.

The present invention economically and simply accomplishes theobjectives of both short and long wheelbases by means of a lower middlewheel 22. For example, when operated over a hard, smooth surface,undercarriage 10 will be able to rock either forwardly or backwardly,depending upon the location of the center of gravity and the loadingcharacteristics of the particular adverse terrain vehicle. The vehiclerests on only two wheels at any given moment, while an end wheel remainsavailable for stabilization. Therefore, the wheelbase of the vehiclewill comprise the distance between the middle wheel 22 and one of theendmost wheels, either 20 or 24. Consequently, the effort required toeffect skid steering of the vehicle is substantially reduced over thatwhich would be required if the wheelbase always comprised the distancebetween the endmost wheels 20 and 24. At the same time, the rockingfeature of undercarriage 10 allows instant utilization of the stabilityinherent in a longer wheelbase.

Assume now that the vehicle to which undercarriage 10 is attached isoperated over a softer surface, such as sand, mud or loose dirt. Allthree tired wheels 18 will engage the adverse surface because they willsink into the adverse surface until vehicle flotation occurs. Superiortraction, stability, and maneuverability will be achieved since eachwheel 18 directly contacts the surface, and all wheels 18 are drivinglyinterconnected. Furthermore, total pressure under any individual wheelis substantially reduced, which lessens surface rutting as well as thevehicle's susceptibility to bogging down.

Turning now to FIGS. 3a and 3b, there is shown in detail the drivesystem for undercarriage 10. Motor 30 is coupled to speed reducer 40.Speed reducer 40 is attached to frame extension 42 by means of bolts 94in conjunction with nuts 96. By means of slots 98, speed reducer 40 isadapted for slidable movement relative to frame extension 42 when actedupon by tension adjusting bolt 58, which is best shown in FIG. 1.Attached to the output shaft 46 of the speed reducer 40 is sprocket 48.Setscrew 49 secures sprocket 48 to output shaft 46. Chain 52 in turnconnects sprocket 48 to sprocket 50. Sprocket 50 is affixed to axle 26of rear wheel 24 by means of nut 100. It will be noted that all threeaxles 26 are rotatably supported by the inner bearing assemblies 102 andouter bearing assemblies 104. Inner bearing assemblies 102 are supportedby cups 106 which are detachably secured to frame 12 by means of bolts108. In contrast, outer bearing assemblies 104 are permanently affixedto frame extensions 82 of frame 12.

Sprocket 62 is also attached to axle 26 of rear wheel 24 by means ofkeyway 110, thus sprocket 62 rotates in unison with sprocket 50.Sprocket 62 in turn is connected by means of chain 64 to sprocket 66,which is secured to axle 26 of middle wheel 22 by means of a keyway 112.Located substantially adjacent to sprocket 66 and also attached to axle26 of middle wheel 22 by means of keyway 112 is sprocket 68. Chain 70 isconstrained for rotation around sprockets 68 and 72. Sprocket 72 isaffixed to axle 26 of forward wheel 20 by means of keyway 114.Consequently, motor 30 is directly connected by a series of sprocketsand chains to each wheel 18 of undercarriage 10.

The tension in chains 64 and 70 is adjusted by means of forward and reartension adjustment assemblies 74. Tension adjustment assemblies 74include idler sprocket 116 which engage the slack or return sides ofeither chain 64 or 70. Idler sprocket 116 is rotatably connected to pin118 by means of journal bearing 120. The pin 118 which rotatablysupports idler sprocket 116 is disposed and secured between two verticaladjacent wall surfaces of slider assembly 122. Slider assembly 122 isconstrained for vertical movement by stops 124 and 126. Verticalmovement of slider assembly 120 is accomplished by means of adjustablescrews 128. Either clockwise or counterclockwise movement of adjustablescrews 128 serves to displace slider assembly 122 vertically, wherebyidler sprocket 116 engages idler chains 64 or 70 so as to change thetension therein. For example, if idler sprocket 116 of forward tensionadjustment assembly 74 were manipulated in a vertical direction, itwould engage chain 70 so as to cause a small but significant increase inthe effective travel distance thereof. This in turn would cause chain 70to experience an increase in tension, because it is of substantiallyfixed length.

Protective covers 130 are provided to protect the inward ends of axles126 of forward wheel 20 and middle wheel 22. Covers 130 are secured tobearing cup 106 by means of screws 132. Consequently, all inward ends ofaxles 26 on undercarriage 10 are shielded from rocks, dirt, mud, orother hazards to be found in the terrain over which the adverse terrainvehicle is likely to operate.

The foregoing description was directed to the preferred construction ofundercarriage 10 wherein each wheel 18 is interconnected by a series ofsprockets and chains. However, it will be understood that undercarriage10 can be operated with other transmission means, such as gears or othermeans; and such that motor 30 is drivingly connected to less than all ofthe wheels 18. For example, motor 30 can be drivingly connected to rearwheel 24 and middle wheel 22 only, thereby eliminating the need forsprockets 68 and 72, chain 70, and forward tension adjustment assembly74 all of which serve to interconnect forward wheel 20 and middle wheel22.

Referring now to FIGS. 4 and 5, there are shown two modifications of thethree wheel undercarriage for an adverse terrain vehicle 10. Referringparticularly to FIG. 4, there is shown an alternative position for thehydrostatic drive assembly 28. The position illustrated in FIG. 4 ishigher and more rearward than that depicted in FIGS. 1 and 2, but stilldisposed substantially between rear wheel 24 and middle wheel 22. Thewheel spacing in FIG. 4 is relatively closer than that shown in FIGS. 1and 2. FIG. 5 illustrates another alternative position for hydrostaticdrive assembly 28 which permits reduced wheel spacing of undercarriage10 over that shown in FIG. 4. In this modification, drive assembly 28 ismounted on rear frame extension 134. The closer wheel placementpermitted by the modifications appearing in FIGS. 4 and 5 facilitatesskid steering of undercarriage 10 because the effort required issubstantially reduced over that which would be required if the wheelbase were longer. Accordingly, not only are the power requirements forsteering the vehicle lowered, but overall vehicle response is improved.Moreover, the feature of being able to vary the wheel spacing and/or thehydrostatic drive housing location considerably enhances theadaptability of undercarriage 10 to virtually any type of adverseterrain vehicle.

Referring now to FIGS. 15 and 16, there is shown another modification ofthe three wheel undercarriage for an adverse terrain vehicle 10. Atleast two significant features attend this modification. First, insteadof supporting hydrostatic drive assembly 28 with a frame extensionattached to the top surface of frame 12, drive assembly 28 is slidablymounted directly on the rear portion of frame 12. Frame 12 in FIGS. 15and 16 includes an integral raised rear portion which serves to houseand protect sprockets 48 and 50, and drive chain 52. Besides eliminatingthe need for a separate housing to protect these parts of the drivesystem, placement of drive assembly 28 on the side of frame 12 oppositewheels 18 makes it less vulnerable to flying rocks, dirt, mud andobjects likely to be picked up by the wheels of the vehicle. Inaddition, this location for drive assembly 28 allows a lower profilewhich further enhances adaptability of undercarriage 10 to various typesof adverse terrain vehicles. Bolt 58 is threadably mounted on brace 60which is now attached directly to the rear top and side portions offrame 12. Bolt 58 acts in tension directly on the collar of speedreducer 40 to serve as a tension adjusting means for chain 52. Theabsence of brake assembly 76 secured to middle wheel 22 comprises thesecond feature of the modification illustrated in FIGS. 15 and 16.Instead, brake assembly 133 is positioned directly between motor 30 andspeed reducer 40. Brake 133 may be of the AUSCO brand fail-safe typeproduced by Auto Specialties Manufacturing Co. of St. Joseph, Mich. Ithas been found that placement of brake 133 in drive assembly 28 requireslower braking effort which results in increased brake efficiency. Ifdesired, access plates (not shown) can be located in the upper surfaceof frame 12 above the axles for wheels 18. In all other respectsundercarriage 10 with the modification shown in FIGS. 15 and 16 operatesas was described above.

Referring now to FIGS. 7 and 8, there is shown an undercarriage for anadverse terrain vehicle 136 incorporating a second embodiment of theinvention. The undercarriage 134 incorporates numerous component partswhich are substantially identical in construction and operation to thecomponent parts of undercarriage 10 illustrated in FIGS. 1 and 2. Suchidentical component parts are designated in FIGS. 7 and 8 with the samereference numeral utilized in the description of undercarriage 10, butare differentiated therefrom by means of a prime (') designation.

The primary differentiation between undercarriage 10 and undercarriage136 is the fact of a four tired wheel embodiment, wherein wheel 138 isthe fourth wheel. The extra wheel 138 is in fact another middle wheel.The middle wheels 22' and 138 extend below plane 92' which is tangent tothe bottom surfaces of wheels 20' and 24'. All wheels 18' are of equaldiameter and include tires of either a solid or a pneumatic type.However, the addition of lower middle wheel 138 requires the addition oftwo more sprockets, 140 and 144, and another chain 142, and maynecessitate an additional brake assembly 76'.

In many respects similar to the three wheel configuration, thetransmission of power in the four wheel configuration shown in FIGS. 7and 8 proceeds as follows. The hydrostatic drive assembly 28' is mountedon the rearmost upper surface of undercarriage 136 and includes motor30'. Motor 30' is connected directly to speed reducer 40'. Attached tothe output shaft 46' of speed reducer 40' is sprocket 48'. Chain 52' isconstrained for rotation about sprockets 48' and 50'. Sprocket 50' inturn is secured to the axle 26' of rear wheel 24'. Also attached to theaxle 26' of rear wheel 24' is sprocket 62'. Connected by chain 64',sprocket 66' is constrained to rotate in unison with sprocket 62'.Sprocket 66' is mounted on axle 26' of middle wheel 22', as is sprocket68'. Chain 142 in turn connects sprocket 140, which is affixed to axle26' on second middle wheel 138, and sprocket 68'. Sprocket 144, which isalso attached to axle 26' of second middle 138, is connected by means ofchain 70' to sprocket 72' which is mounted on axle 26' of forward wheel20'. Thus, it is apparent that motor 30' is in direct mechanicalcommunication with all four wheels of undercarriage 136 by virtue of theaforementioned arrangement of sprockets and chains. It will beunderstood that undercarriage 136 can be operated where motor 30' isdrivingly connected to fewer than all four wheels. Note also thathydrostatic drive guard 146 is provided at a rearward lower position onundercarriage 136 adjacent to drive assembly 28' so as to protect itfrom the hazards of operation over adverse terrain. In all otheraspects, the four wheel embodiment illustrated in FIGS. 7 and 8 operatessubstantially the same as the three wheel embodiment shown in FIGS. 1and 2.

In certain applications, it may be desirable to adjust the height of anend wheel of undercarriage 10, or one or both end wheels ofundercarriage 136. Referring now to FIG. 10, there is shown a wheelheight adjustment assembly 148. Adjustment assembly 148 comprises asubframe 150 which is pivotally attached to frame 12 at pin 152. Theoutside vertical walls of subframe 150 are interposed between the insidevertical walls of frame 12 so as to allow connection at, and pivotalmovement about, pin 152. A hydraulic cylinder 154 is attached at one endto a frame 156 mounted on frame 12, and at the other end to a frame 158mounted on subframe 150. A boot 160 of highly resilient, flexiblematerial is securely attached to seal the gap existing between frame 12and subframe 150. When actuated, cylinder 154 causes subframe 150 topivot downwardly about pin 152 so as to bring into alignment the axes ofrotation of wheels 18. Turning momentarily to FIGS. 1 and 2 inconjunction with FIG. 10, it will be seen that provision has been madefor the incorporation of one wheel height adjustment assembly 148 in thethree wheel embodiment shown therein, at the location indicated by arrow148a. Wheel height adjustment assembly 148 is positioned between forwardwheel 20 and middle wheel 22. Upon actuation of hydraulic cylinder 154,subframe 150 will pivot downwardly about pin 152 so as to bring the axesof rotation of wheels 20, 22 and 24 into alignment.

In contrast to the three wheel embodiment of undercarriage 10, two wheelheight adjustment assemblies 148, indicated by arrows 147 and 149, canbe incorporated in the four wheel embodiment of undercarriage 136.Having reference momentarily to FIGS. 7 and 8 in conjunction with FIG.10, it will be seen that forward wheel height adjustment assembly 148 islocated between forward wheel 20' and middle wheel 138, while rear wheelheight adjustment assembly 148 is positioned between rear wheel 24' andmiddlle wheel 22'. Upon actuation of hydraulic cylinder 154 of forwardwheel height adjustment assembly 148, subframe 150 will pivot downwardlyto bring into alignment the axes of rotation of the forward three wheelsof undercarriage 136. Similarly, the axes of rotation of the rearwardthree wheels of undercarriage 136 will become aligned upon the urging ofcylinder 154 of rear wheel height adjustment assembly 158. Thesimultaneous actuation of cylinders 154 in both assemblies will causethe axes of rotation of all four wheels 18' to come into alignment.

The incorporation of wheel height adjustment assemblies 148 affords asignificant advantage in both the three and four wheel lowered centerwheel embodiments of the invention. Primarly it will effect betterweight distribution and hence impart greater vehicle stability. Inparticular, during operation of the adverse terrain vehicle over a hardsurface, the operator may selectively lower the end wheel or wheelsshould the skid steering advantages of a shoft wheelbase no longer bedesired. For example, it might be desirable to stabilize a mobile drillrig incorporating the invention after the vehicle had been maneuveredinto place. The capability of selectively nullifying the rocking featureof the present invention is particularly useful to vehicles whose centerof gravity shifts during various operational modes. It will beunderstood that soft surface operation of a vehicle incorporating theinvention is the same with or without the wheel height adjustmentfeature. All wheels will contact the soft surface, thus improving thevehicle's traction and flotation characteristics.

With reference to FIG. 17, there is shown an undercarriage for anadverse terrain vehicle 210 incorporating a third embodiment of theinvention. The undercarriage 210 includes numerous component parts whichare substantially identical in construction and operation to thecomponent parts of undercarriage 10 illustrated in FIGS. 1 and 2. Suchidentical component parts are designated in FIG. 17 with the samereference numeral utilized in the description of undercarriage 10, butare differentiated therefrom by means of a double prime (") designation.

The primary distinction between undercarriage 210 and undercarriage 10is the fact of a three tired wheel embodiment wherein the diameters ofthe wheels 18" are not identical. More particularly, middle wheel 22" isof relatively larger diameter than are the endmost wheels 20" and 24".Additionally, each wheel 18" rotates about an axle lying on a commonline of centers, which is denoted by line 212. Thus, larger middle wheel22" still protrudes below the plane 92" extending tangent to the bottomsurfaces of forward wheel 20" and rear wheel 24", but for completelydifferent reasons than its counterpart in undercarriage 10.

The fact of an aligned larger center wheel comprises a significantfeature of this embodiment. The objectives of both a short and a longwheel base is accomplished by means of larger middle wheel 22". Forexample, when operated over a hard, smooth surface, undercarriage 210will be able to rock either forwardly or backwardly, depending upon thelocation of the center of gravity and the loading characteristics of theparticular adverse terrain vehicle. The vehicle rests on only two wheelsat any given moment, while the other wheel remains available forstabilization. Consequently, the wheel base of the vehicle when operatedover a hard, smooth surface is the distance between wheel 22" and one ofthe end most wheels, either 20" or 24". The effort required to effectskid steering of the vehicle is substantially reduced with a shorterwheel base, while the rocking feature of undercarriage 210 allowsrecourse to the stability inherent with a longer wheel base. It will benoted that if middle wheel 22" includes a pneumatic tire, the partialdeflation thereof will serve to neutralize the rocking feature and bringall three wheels 18" into contact with the hard, smooth surface toimprove vehicle traction and stability. Conversely, greater inflation ofmiddle wheel 22' will serve to augment the rocking feature, if desired.Of course, during operation of undercarriage 210 over a softer surface,all three tired wheels 18" engage the adverse surface because they willsink into the surface until vehicle flotation occurs. Moreover,alignment of the axles of wheels 18" improves the vehicle performanceover both hard and soft surfaces by reducing propoising and othercontrol problems associated with multiple nonaligned drive wheels. Thepower transmission and other aspects of the aligned three wheelembodiment illustrated in FIG. 17 are substantially identical to that ofthe nonaligned three wheel embodiment shown in FIGS. 1 and 2, and themodifications thereof, which were discussed hereinbefore.

FIGS. 19-23 illustrate further modifications of the three-wheelundercarriage herein. These modifications comprise alternative drive andtransmission arrangements which can be used with undercarriage 10 havingwheels of substantially equal size, as well as with undercarriage 210having a relatively larger middle wheel. The modifications shown inFIGS. 19-23 thus serve to extend the usefulness of the invention byfacilitatinng adaptability thereof to a wider variety of mechanisms andvehicles. It will be understood that operation of undercarriagesincorporating these modifications is substantially unchanged over thatdescribed hereinabove.

FIG. 19 shows an undercarriage 10 with a drive assembly 28 having atleast one motor 240 and one or more planetary gear boxes 242. Aplanetary gear box 242 can be provided for each of the wheels 20, 22 and24. Gear boxes 242 are of conventional construction and may be providedwith external or internal brakes (not shown). For example, planetarygear boxes of the type manufactured by Clark Equipment Company ofBuchanan, Mich. may be suitable for use as gear boxes 242.

Motor 240 and gear box 242 in wheel 24 are interconnected by shaft 244.Shaft 244 can comprise the output shaft of motor 240, the input shaft ofgear box 242, a cross-shaft within frame 12 to which the motor and gearbox are coupled or axle of wheel 24. Sprocket 246 is secured to shaft244. A chain 248 interconnects sprocket 246 with a sprocket 250 mountedon a shaft 252 which is coupled to gear box 242 for middle wheel 22.Sprocket 254, which is mounted on shaft 252, is connected by chain 256to a sprocket 260 mounted on a shaft 258, to which planetary gear box242 for forward wheel 20 is coupled. Shafts 252 and 258 can compriserotatable shafts within frame 12 the output shafts of gear boxes 242, orthe axles of wheels 22 and 20. It will thus be apparent that wheels 20,22 and 24 of undercarriage 10 can be selectively driven by one motor 240acting through a chain and sprocket transmission and a plurality ofplanetary gear boxes 242.

As indicated with phantom lines in FIG. 19, separate motors 240 can beprovided for wheels 20 and 22 of undercarriage 10 if desired. Each wheelon undercarriage 10 would thus be individually driven in unison by amotor 240 and a planetary gear box 242, in which case the chain andsprocket arrangement interconnecting the wheels would not be required,but could be

FIG. 19 shows an undercarriage 10 with a drive assembly 28 having atleast one motor 240 and one or more planetary gear boxes 242. Aplanetary gear box 242 can be provided for each of the wheels 20, 22 and24. Gear boxes 242 are of conventional construction and may be providedwith external or internal brakes (not shown). For example, planetarygear boxes of the type manufactured by Clark Equipment Company ofBuchanan, Mich. may be suitable for use as gear boxes 242.

Motor 240 and gear box 242 in wheel 24 are interconnected by shaft 244.Shaft 244 can comprise the output shaft of motor 240, the input shaft ofgear box 242, a cross-shaft within frame 12 to which the motor and gearbox are coupled or axle of wheel 24. Sprocket 246 is secured to shaft244. A chain 248 interconnects sprocket 246 with the sprocket 250mounted on a shaft 252 which is coupled to gear box 242 for middle wheel22. Sprocket 254, which is mounted on shaft 252, is connected by chain256 to a sprocket 260 mounted on a shaft 258, to which planetary gearbox 242 for forward wheel 20 is coupled. Shafts 252 and 258 can compriserotatable shafts within the frame 12 the output shafts or gear boxes242, or the axles of wheels 22 and 20. It will thus be apparent thatwheels 20, 22 and 24 of undercarriage 10 can be selectively driven byone motor 240 acting through a chain and sprocket transmission and aplurality of planetary gear boxes 242.

As indicated with phantom lines in FIG. 19, separate motors 240 can beprovided for wheels 20 and 22 of undercarriage 10 if desired. Each wheelon undercarriage 10 would thus be individually driven in unison by amotor 240 and a planetary gear box 242, in which case the chain andsprocket arrangement interconnecting the wheels would not be required,but could be used to assure constant speed of all wheels and to transmitpower to the wheel or wheels that are developing traction.

In some situations, it may be desirable to substitute a motor and speedreducer for each motor 240 in undercarriage 10 of FIG. 19 instead ofusing a planetary gear box 242 for each wheel thereof. Shafts 244, 250and 258 would therefore correspond to the axles of wheels 24, 22 and 20,respectively. The wheels of undercarriage 10 can thus be drivinglyinterconnected by a chain and sprocket arrangement and drivensimultaneously by a single drive means coupled directly to one of theaxles.

FIG. 20 shows an undercarriage 10 similar to that shown in FIG. 19,except that an angle or bevel drive gear arrangement is employed tointerconnect motor 240 with planetary gear boxes 242. Motor 240 may bean electric or hydraulic motor of suitable torque and speed capacity.Angle drive gears 262, 264 and 266 are mounted on shafts 244, 250 and258, respectively, instead of sprockets. A drive shaft 268 having angleor bevel gears at the ends thereof drivingly interconnects gears 262 and264, and a similar drive shaft 270 in turn connects gear 264 to gear266. It will thus be apparent that the wheels of undercarriage 10 can bedriven by one motor 240 coupled to a plurality of planetary gear boxes242 through a drive gear arrangement.

In some situations, it may be desirable to substitute a motor and speedreducer for motor 240 in undercarriage 10 of FIG. 20 instead of using aplanetary gear box 242 for each wheel thereof. Shafts 244, 250 and 258would therefore correspond to the axles of wheels 24, 22 and 20,respectively. The wheels of undercarriage 10 can thus be drivinglyinterconnected by an angle gear arrangement and driven simultaneously bya single drive means.

FIG. 21 shows an undercarriage 10 incorporating a spur gear drivearrangement. Spur gears 272, 274 and 276 are mounted on shafts 244, 250and 258, respectively, instead of sprockets or angle gears. A number ofidler gears 278, each being supported for rotation on a cross shaftwithin frame 12, are enmeshed between spur gears 272 and 276 and spurgear 274. Planetary gear boxes 242 may be unnecessary upon substitutionof motor 240 with a sufficiently high torque motor or a motor togetherwith a speed reducer. It will thus be apparent that the wheels ofundercarriage 10 can be drivingly interconnected by a spur geararrangement and driven simultaneously by a single drive means.

FIG. 22 illustrates a pair of undercarriages 10 driven by a single motor280 through one differential drive 282. One differential drive isprovided for one pair of opposite wheels on undercarriages 10. Anysuitable type of motor can be used as motor 280, and differential drive282 may be a transaxle of the type which is commercially available inthe automotive industry. A suitable unit for drive 282 is shown in FIG.24 and will be described hereinafter. A planetary gear box 284 and brake286 can be provided for each wheel of each undercarriage 10 as shown;however, gear boxes and brakes can be provided only for wheels 24 ifdesired. In the alternative, two planetary gear boxes 284 could becoupled between differential drive 282 and undercarriages 10 at thelocations indicated by arrows 288. Brakes 286 may be of the disc type,as illustrated, or the drum type.

The wheels of each undercarriage 10 in FIG. 22 are drivinglyinterconnected by a chain and sprocket arrangement. Sprockets 290 aremounted on the ends of shafts 292 of differential drive 282. Shafts 292are connected to planetary gear boxes 284 for end wheels 24 inundercarriages 10. Sprocket 290 is connected by chain 294 to sprocket296 on shaft 298, which is coupled to the planetary gear box 284 formiddle wheel 22 of each undercarriage 10. Sprockets 300, which are alsomounted on shafts 298, are connected by chains 302 to sprockets 304 onshafts 306 of the other end wheels 20. It will thus be apparent that apair of undercarriages including transmissions can be driven by a commonmotor and differential drive unit.

If desired, the angle drive gear arrangement of FIG. 20, or the spurgear arrangement of FIG. 21, could be utilized in place of the chain andsprocket transmissions in undercarriages 10 of FIG. 22.

FIG. 23 illustates a pair of undercarriages 10 coupled to threedifferential drives 282 and driven by one motor 280. One differentialdrive is provided for each pair of end wheels 20, each pair of middlewheels 22 and each pair of end wheels 24. The differential drives 282are drivingly interconnected by shafts 308. A hydraulic motor or othersuitable type of motor can be used for motor 280. A brake 286 isprovided for each separate wheel. Similarly, a planetary gear box 284can be provided for the wheels on each undercarriage 10 if desired.Transmission means inside frames 12 are not necessary with the drivearrangement shown in FIG. 23. It will thus be apparent that multipledifferential drive units can be employed to effect rotation of thewheels on a pair of undercarriages 10.

The constructional details of differential drive 282 and planetary gearbox 284 are shown in FIG. 24. Drive 282 and gear box 284 are ofconventional construction, and may be combined in one commerciallyavailable unit such as the Model BD-100000 planetary drive bogey axlemanufactured by Clark Equipment Company of Buchanan, Mich.

Drive shaft 308, or the output shaft of motor 280, is connected to anupper pinion gear (not shown) engaged with a lower pinion gear 310 ofdrive 282. Pinion gear 310 is mounted on a shaft 312 supported bybearings 314 in housing 316 of axle 282. A bevel gear 318 is alsomounted on shaft 312. Rotation of gear 318 is transferred to shafts 320by means of a ring gear 322.

Bearings 324 support shafts 320 within housing 316. Each shaft 320 issecured to a pinion gear 326 within planetary gear box 284. Threeplanetary gears 328, only one of which is shown, are enmeshed betweengear 326 and a ring gear 330 on housing 332 of gear box 284. Housing 332is supported for rotation about spindle 334 by bearings 336. Spindle 334surrounds shaft 320 and is anchored to housing 316 of axle 282. A wheel(not shown) mounted on gear box housing 332 is therefore drivenresponsive to rotation of shaft 320.

A drum type brake 338 is secured to spindle 334 and actuates against theinside end of gear box housing 332. Brake 338 is of conventionalconstruction, and may comprise, if desired, a disc type brake such asbrake 286 shown in FIGS. 22 and 23. Brake 338 includes a drum 340 whichis secured to gear box 284 for rotation therewith. Brake 338 isselectively applied by means of pneumatic actuator 342 acting through acontrol rod 344.

Turning now to FIG. 18, there is shown an undercarriage for an adverseterrain vehicle 230 incorporating a fourth embodiment of the invention.The undercarriage 230 includes numerous component parts which aresubstantially identical in construction and operation to the componentparts of undercarriage 136 illustrated in FIGS. 7 and 8. Such identicalcomponent parts are designated in FIG. 18 with the same referencenumeral utilized in the description of undercarriage 136, but aredifferentiated therefrom by means of a triple prime ("') designation.

The primary distinction between undercarriage 230 and undercarriage 136is the fact of a four tired wheel embodiment wherein the diameters ofthe wheels 18" are not identical. More particularly, middle wheels 22"'and 232 are of relatively larger diameter than are the endmost wheels20"' and 24"'. Additionally, each wheel 18"' rotates about an axle lyingon a common line of centers, which is denoted by line 234. Thus, largermiddle wheels 22"' and 232 protrude below the plane 92"' extendingtangent to the bottom surfaces of forward wheel 20"' and rear wheel24"', but for completely different reasons than their counterparts inundercarriage 136.

The fact of aligned larger center wheels comprises a significant featureof this embodiment. The objectives of both a short and a long wheel baseis accomplished by means of larger middle wheels 22"' and 232. Forexample, when operated over a hard, smooth surface, undercarriage 230will be able to rock either forwardly or backwardly, depending upon thelocation of the center of gravity and the loading characteristics of theparticular adverse terrain vehicle. The vehicle rests on only threewheels at any given moment, while the other wheel remains available forstabilization. Consequently, the wheel base of the vehicle when operatedover a hard, smooth surface is the distance between wheels 22"' and 232and one of the endmost wheels, either 20"' or 24"'. Therefore, theeffort required to effect skid steering of the vehicle is substantiallyreduced with a shorter wheel base, while the rocking feature ofundercarriage 230 allows recourse to the stability inherent with alonger wheel base. It will be noted that if the center wheels 18"'include pneumatic tires, the partial deflation thereof will serve toneutralize the rocking feature to bring all four wheels 18"' intocontact with the hard, smooth surface improving vehicle traction andstability. Conversely, greater inflation of middle wheels 22"' and 232will serve to augment the rocking feature, if desired. Of course, duringoperation of undercarriage 230 over a softer surface, all four tiredwheels 18"' engage the adverse surface because they will sink into thesurface until vehicle flotation occurs. Moreover, alignment of the axlesof wheels 18"' improves the vehicle performance over both hard and softsurfaces by reducing propoising and other control problems associatedwith multiple nonaligned drive wheels. The power transmission and otheraspects of the aligned four wheel embodiment illustrated in FIG. 18 issubstantially identical to that of the nonaligned four wheel embodimentdepicted in FIGS. 7 and 8, and the modifications thereof, which werediscussed previously.

Referring now to FIG. 9, there is shown a T-handle 162 which can bemounted in the cockpit of the adverse terrain vehicle to which theinvention is attached. T-handle 162 performs the function of controllingthe flow of energy from a remote source (not shown) to the motor(s) ofthe hydrostatic drive system. The T-handle 162 is supported for pivotalmovement about horizontal and vertical axes 164 and 166, respectively.The handle 162 includes a pair of handle grips 168 and a lower portion170 extending parallel to handle grips 168. Thus, manipulation of thehandle grips 168 relative to axles 164 and 166 results in a directlycorresponding motion in lower handle portion 170.

The lower handle portion 170 of the T-handle 162 is coupled to a pair oflevers 172 by means of a pair of links 174. The levers 172 serve tocontrol the energy flowrate to the motors. In this way, the T-handle 162is operable to provide complete control over the direction, speed, andsteering of the vehicle incorporating the invention. Manipulation of theT-handle 162 solely about the horizontal axis 164 causes movement ofboth the levers 172 in the same direction by the same amounts. By thismeans, the motors are actuated in synchronism for propulsion of thevehicle either forwardly or rearwardly along a straight line. Similarly,manipulation of T-handle 162 solely about the vertical axis 166 causesequal and opposite flow of motive energy to the motors whereby thevehicle pivots about its center, but does not move either forward orrearward. Of course, any combination of manipulation about axes 164 and166 is possible to effect complete control of the adverse terrainvehicle. A pair of springs 176 are provided for returning the levers 172to their center or nil position wherein the remote power source (notshown) provides no output to the motors.

In reference now to FIGS. 11-14, there are shown several vehicles towhich either the lowered center wheel(s) or larger center wheel(s)embodiments of the undercarriage of the present invention can beadapted. Although each vehicle has a different operational and loadingprofile, the present invention is equally compatible with all. It willbe understood that wheel height adjustment assemblies 147 and 149, or148 can be adapted to each vehicle utilizing lowered center wheels toimpart additional stability, if desired.

FIG. 11 illustrates application of the undercarriage 10 to a front-endloader 178. The heaviest component of the machine, the engine 180, islocated to the rear of the vehicle. In the unloaded condition, with thebucket 182 retracted and empty, the center of gravity is locatedrearward near the engine 180 so that the vehicle rests on its rear andmiddle pairs of wheels. After loading and upon extension of the unloadedbucket 182, the center of gravity shifts forward, which causes thevehicle to rock forward to rest upon its forward and middle pairs ofwheels.

Shown in FIG. 12, born by undercarriage 10, is a front-end loaderequipped with a backhoe 184. The engine 186 is mounted forward. Thecenter of gravity will be located forward near the engine 186 when theempty front-end loader 188 is retracted, and the empty backhoe 190 istucked in. The vehicle in the unloaded configuration will thus besupported by its forward and middle sets of wheels. If the front-endloader 188 alone is loaded and extended, the vehicle's center of gravityremains forward and the vehicle will continue to rest on its forward andmiddle pairs of wheels. If only the backhoe 190 is manipulated, thecenter of gravity will shift rearward causing the vehicle to rock backand rest on its rearward and middle pairs of wheels. Of course, duringcombined operation of the front-end loader 188 and the backhoe 190, thevehicle may rock either forwardly or rearwardly depending on therelative loads manipulated.

FIG. 13 depicts undercarriage 136 as applied to a mobile drilling rig192. During transportation, the drilling mast 194 lies substantiallyparallel to the vehicle. The weight of the mast 194 when added to thatof the forwardly located engine 196 causes the vehicle to rest upon itsforward and middle pairs of wheels. Upon raising mast 194 into drillingposition, the center of gravity shifts rearward to reposition thevehicle on the rearward and middle sets of wheels.

Another backhoe 198 is shown in FIG. 14 supported on undercarriage 136.Owing to the rearward engine 200 location, the vehicle rests on itsrearward and middle pairs of wheels when the bucket 202 is tucked in andempty. During manipulation of the bucket 202, the vehicle rocks forwardto be supported by the forward and middle pairs of wheels.

While each of the example applications of the invention appearing inFIGS. 11-14 was discussed above as though the vehicle were operatingover hard, smooth terrain, it will be understood that while operatingover softer terrain, all wheels would contact the surface, achievingbetter flotation and traction.

Thus it is apparent that there has been provided, in accordance with theinvention, an undercarriage for an adverse terrain vehicle that fullysatisfies the objects, aims and advantages set forth above. While theinvention has been described in conjunction with specific embodimentsthereof, it is evident that many alternatives, modifications, andvariations will be apparent to those skilled in the art in view of theforegoing description. Accordingly, it is intended to embrace all suchalternatives, modifications, and variations as fall within the spiritand scope of the invention.

What is claimed is:
 1. An undercarriage assembly for supporting andpropelling a mechanism, comprising:an elongate hollow load-bearing frameadapted for connection to the mechanism; at least three axle memberseach having a wheel receiving member at one end thereof; at least threewheel members each mounted on and secured to a wheel receiving end of anaxle member outside said frame; means rotatably supporting the axlemembers at longitudinally spaced points along the frame with each of theaxle members extending through the frame and being rotatably supportedin opposite sides of said frame; the middle wheel member extending belowa plane lying tangent to the bottoms of the endmost wheel members tofacilitate skid steering of the mechanism; transmission means positionedwithin the frame for drivingly interconnecting the middle axle memberwith at least one of the endmost axle members; drive means operablyconnected to the transmission means for actuation thereof whereby thedrive means and the transmission means cause concurrent rotation of theinterconnected axle members; and said transmission means furtherincluding a planetary gearset drivingly interconnecting each axle andthe wheel mounted thereon.
 2. The undercarriage assembly according toclaim 1 wherein the drive means includes a motor drivingly connected toeach wheel, and where the transmission means contrains the wheels torotation at the same speed.
 3. An undercarriage assembly for supportingand propelling a mechanism, comprising:an elongate hollow load-bearingframe adapted for connection to the mechanism; at least three axlemembers each having a wheel receiving member at one end thereof; atleast three wheel members each mounted on and secured to a wheelreceiving end of an axle member outside said frame; means rotatablysupporting the axle members at longitudinally spaced points along theframe with each of the axle members extending through the frame andbeing rotatably supported in opposite sides of said frame; the middlewheel member extending below a plane lying tangent to the bottoms of theendmost wheel members to facilitate skid steering of the mechanism;transmission means positioned within the frame for drivinglyinterconnecting the middle axle member with at least one of the endmostaxle members; drive means operably connected to the transmission meansfor actuation thereof whereby the drive means and the transmission meanscause concurrent rotation of the interconnected axle members; and saidtransmission means comprising driving shaft means mounted within theframe for drivingly interconnecting at least two of the axles.
 4. Theundercarriage assembly according to claim 3 wherein the drive shaftmeans comprises two drive shafts each drivingly interconnecting themiddle axle and one of the endmost axles.
 5. An undercarriage assemblyfor supporting and propelling a mechanism, comprising:an elongate hollowload-bearing frame adapted for connection to the mechanism; at leastthree axle members each having a wheel receiving member at one endthereof; at least three wheel members each mounted on and secured to awheel receiving end of an axle member outside said frame; meansrotatably supporting the axle members at longitudinally spaced pointsalong the frame with each of the axle members extending through theframe and being rotatably supported in opposite sides of said frame; themiddle wheel member extending below a plane lying tangent to the bottomsof the endmost wheel members to facilitate skid steering of themechanism; transmission means positioned within the frame for drivinglyinterconnecting the middle axle member with at least one of the end mostaxle members; drive means operably connected to the transmission meansfor actuation thereof whereby the drive means and the transmission meanscause concurrent rotation of the interconnected axle members; and saidtransmission means being further characterized by axle gears drivinglyconnected to the middle axle and at least one endmost axle and at leastone idler gear drivingly interconnecting the axle gears.
 6. Theundercarriage assembly according to claim 5 wherein all three axles aredrivingly interconnected by gears mounted within the frame.
 7. Anundercarriage assembly for supporting and propelling a mechanism,comprising:an elongate hollow load-bearing frame adapted for connectionto the mechanism; at least three axle members each having a wheelreceiving member at one end thereof; at least three wheel members eachmounted on and secured to a wheel receiving end of an axle memberoutside said frame; means rotatably supporting the axle members atlongitudinally spaced points along the frame with each of the axlemembers extending through the frame and being rotatably supported inopposite sides of said frame; the middle wheel member extending below aplane lying tangent to the bottoms of the endmost wheel members tofacilitate skid steering of the mechanism; transmission means positionedwithin the frame for drivingly interconnecting the middle axle memberwith at least one of the endmost axle members; drive means operablyconnected to the transmission means for actuation thereof whereby thedrive means and the transmission means cause concurrent rotation of theinterconnected axle members; and said drive means including a drivemotor and a differential gearset, said differential gearset drivinglyinterconnecting the drive motor and the transmission means.